STUDIES ON BRAIN GANGLIOSIDES. II. ANALYSIS OF HUMAN BRAIN GANGLIOSIDE FRACTIONS OBTAINED BY PREPARATIVE THIN-LAYER CHROMATOGRAPHY

Studies on human platelet gangliosides

Gangliosides, glycosphingolipids which contain sialic acid, were studied in human platelets. They represented 0.5% of the platelet lipids and accounted for 6% of the total neuraminic acid content of platelets. Three major ganglioside fractions were identified and characterized. Ganglioside I was hematoside (G(6)) and comprised 92% of the platelet gangliosides. It contained glucose, galactose, and sialic acid in molar ratios of 1:1:1 and no hexosamine. The major fatty acid was behenate (22:0). Ganglioside I was also identified in isolated platelet granules and membranes. Ganglioside II (5%) contained glucose, galactose, sialic acid, and hexosamines (molar ratios 1:2:1:1). The hexosamines were glucosamine (72%) and galactosamine (28%). It was therefore designated as ganglioside lacto-N-neotetraose. Ganglioside III (2%) contained disialosyllactosyl ceramide (G(3A)) as well as two other gangliosides which could not be precisely characterized. Gangliosides I, II, and III were susceptible to the action of Clostridium perfringens neuraminidase as evidenced by full recovery of sialic acid in its free form after incubation. Neutral platelet glycolipids were qualitatively examined by thin-layer chromatography. The major component was lactosyl ceramide. Interactions of gangliosides I and III and serotonin-(14)C were examined in an equilibrium dialysis system at 4 degrees C. The gangliosides bound serotonin-(14)C in relatively small quantities, whereas control lipids were negative. The binding was essentially unchanged by reverse dialysis, ultracentrifugation and subsequent thin-layer chromatography. The results are comparable to the previously observed nonmetabolic interactions between whole platelets and serotonin in the cold. It is suggested that the orientation and specific distribution of platelet membrane glycolipids may be important determinants of the unique surface properties of platelets.

STUDIES ON BRAIN GANGLIOSIDES: IV. THE EFFECT OF HYPERCAPNIA ON GANGLIOSIDES IN VIVO

Gangliosides are relatively stable acidic glycolipid components of neuronal membranes. When isolated and purified from normal human, rat, or cat brains, they contain 1 μmole of N-acetylneuraminic acid (NANA) per mg. Gangliosides, isolated and purified from fresh autopsy specimens of human brain of patients who were cyanotic before death, contained considerably less NANA and N-acetyl-galactosamine than normal brain gangliosides. Also, gangliosides isolated from cerebral tissue adjacent to a variety of intracerebral lesions contained less NANA than gangliosides from uninvolved tissue from the same patient. Gangliosides from the brains of cats which had been asphyxiated for periods up to 8 minutes also contained less NANA and hexosamine. Experiments in which cats were treated with various gas mixtures showed that hypercapnia and the consequent respiratory acidosis were the major causes of the change in ganglioside composition in vivo. Treatment with 100% N2produced a respiratory alkalosis but had no effect on brain ganglioside composition. The mechanism by which hypercapnia causes the change in the composition of the membrane gangliosides is unclear. An intact cerebral circulation appeared necessary to elicit the changes. The possibility that hypercapnia releases enzyme activators (e.g. adrenalin) or activates brain glycosidases is discussed. The loss of anionic groups located in the neuronal membrane would alter the behavior of these lipids towards cations and may, in part, explain the altered excitability of neurones following hypercapnia.